Abstract/Summary The development of a multicellular organism poses an extraordinary challenge for metabolism, which must fuel dynamic processes from cell growth, division and motility to differentiation and tissue formation. The scientific premise of our R21 proposal is that developmental processes have distinct metabolic signatures due to changing energetic burdens. After fertilization, all metazoan embryos undergo a specialized program of reductive cleavage divisions that produce numerous blastula cells without volumetric growth of the embryo. The field currently lacks critical knowledge about metabolism that would explain how embryonic cells provide the energy and cellular resources to support replication, mitosis and the formation of new cells. This intense period of cell proliferation is fueled by oxidative phosphorylation rather than glycolysis, which drives fast proliferation in cancer cells and stem cells. Thus, development cannot be fully understood without knowledge of the energetics and metabolism of early embryogenesis. How and why is this unique embryonic metabolic strategy deployed? We will establish non-invasive methods ? isothermal calorimetry (ITC) and microrespirometry ? that profile the metabolism of early embryogenesis with high sensitivity and temporal resolution. We provide preliminary evidence in zebrafish that embryonic heat dissipation rates increase during the reductive cleavage divisions. Surprisingly, heat dissipation rates also oscillate with a period that matches the cell cycle, indicating energetic changes during S and M phase. We will investigate the cellular processes underlying the oscillatory and increasing heat dissipation rates during early embryogenesis, quantify their total energetic cost, and determine their efficiency. In doing so, we will calculate and model the embryonic dynamic energy budget (DEB) with quantitative rules for the organization of metabolism that can be understood from basic principles. This systems biology view will be combined with cellular morphometry to integrate metabolism with underlying cellular events, such as cell growth and regulation of mitochondrial activity. Knowledge of the vertebrate embryo DEB can be used to investigate how cellular and molecular processes are coupled to and regulated by metabolism. The establishment of our non-invasive methods in zebrafish, frog and mouse embryos lays the groundwork for investigating energetics and applying the DEB concept to development and disease.